The author s feeling about a subject or topic, which is evidenced in word choice, is called tone.
Carbon tetrahydride is B. CH4
A.is an example of decomposition reaction.
Choices 'C' and 'D' are both correct.
(Except in 'C', changing the temperature from 1°C to 3°C is not usually
described as 'cooling', and it's not the water's 'mass' that changes. But
water does contract in volume during that change.)
